None of the stuff will cross over to the L series.
You can get a good 200+ hp out of that U20... but as Ira said... the damn bearings dont hold up too well. You really have to keep the revs below 6800.
We've though about doing an L20 swap as well... but just have too many projects lined up.
As far as the tranny... I'll have to talk to my uncle, but I THINK there is something you can do.